The invention relates to a casting component for a device for casting or handling a metal melt, the component having a metallic basic body and a surface region which is exposed to the metal melt during casting operation, and to a method for the application of an anticorrosive layer to a substrate, which may be, in particular, the casting component.
Casting components of this type are used in metal casting technology in many different forms, for example as casting fittings, casting vessels, melt furnaces, melt conveyor units and casting molds and also parts of these metal casting constituents. A steel material is mostly used for the basic body, since components of this type possess a good cost/benefit ratio.
It became clear, however, that casting components made from steel, in regions where they come into contact with the hot metal melt during casting operation, are attacked chemically by the liquid metal melt, that is to say are subject to corrosion. Thus, for example, it is observed, in aluminum diecasting, that aluminum melts noticeably attack corrosively those steel surfaces of casting components which come into contact with these melts. To remedy this, it is known, for casting piston/casting cylinder units of metal diecasting machines, to manufacture the casting piston and the casting cylinder entirely from a ceramic material or from a sintered material, for example from sintered titanium diboride (TiB2). However, mechanical strength, heat resistance and shock resistance have still been unsatisfactory. It is proposed as a remedy, in laid-open publication DE 2 364 809, to manufacture the casting piston and the casting cylinder as a composite sintered component from a mixture of two or more substances from the substance group which comprises the carbides, borides and nitrides. In particular, a special mixture of boron carbide (B4C) with one or more of TiB2, zirconium diboride (ZiB2) and boron nitride (BN) is specified.
From patent specification U.S. Pat. No. 4,556,098, this and other sintered materials investigated continue to be designated as unsatisfactory, and alternatively a hot-pressed ultrahard silicon nitride or sialon material of high density is proposed for the casting cylinder and casting piston. For a crucible made from cast iron, a protective coating against corrosion and oxidation, composed of Ca, Al2O2 or other oxides, such as Al2O2—TiO2, or of TiB2, ZaB2, CaB2 or other pure or mixed borides, or of AlN, Si3N4, BN, sialons or other nitrides, is specified, which is applied, for example, from an emulsion or by flame spraying. For conical plugs to close access bores for the rising duct and other parts of a casting fitting, manufacture from such likewise corrosion-resistant and erosion-resistant materials is proposed. For parts of the casting mold which are exposed to the metal melt at only lower temperatures, a coating made from a dense material composed of Si3N4, AlN, sialon, BN, graphite or pyrolytic carbon or alloys thereof is proposed.
It is an object of the invention to provide a casting component of the type initially mentioned and a method for the application of a corrosion layer to a substrate, which may be, in particular, a casting component, the casting component being capable of being produced at relatively low outlay and exhibiting high corrosion resistance for liquid metal casting melts, and, by means of the method, an anticorrosive layer with high corrosion resistance particularly with respect to hot metal melts being capable of being applied comparatively simply and with good layer homogeneity even at locations where access is difficult.
The invention solves this problem by providing a casting component comprising a metallic basic body and a melt contact surface region which is exposed to the metal melt during casting operation, wherein the metallic basic body is provided in the melt contact surface region with an anticorrosive layer which is resistant to the metal melt and which is formed, using at least one of microparticles or nanoparticles of one or more substances from a substance group which comprises borides, nitrides and carbides of the transition metals and their alloys and also boron and silicon and Al2O3, and by providing an anticorrosive layer application method comprising a sol/gel process, using at least one of microparticles or nanoparticles with an average particle size of between 100 nm and 30 μm as a filler.
In the casting component according to the invention, the metallic basic body is provided, in the melt contact surface region in which it is exposed to the metal melt during casting operation, with an anticorrosive layer which is resistant to the metal melt and which is characteristically formed, using microparticles and/or nanoparticles of one or more substances from a substance group which comprises borides, nitrides and carbides of the transition metals and their alloys and also of boron and silicon and of Al2O3. Investigations have shown that a casting component equipped with this special anticorrosive layer exhibits unexpectedly good corrosion resistance with respect to contact with hot reactive metal melt, precisely also with respect to aluminum melts. This is assumed to be explained primarily by the presence of one or more anticorrosive substances in the form of microparticles and/or nanoparticles in the layer. In particular, investigations have shown that casting components coated in this way have very high corrosion resistance with respect to aluminum melts and a correspondingly long service life which may be superior to that of identical components which are composed entirely of a steel material or a ceramic material or which are provided conventionally with an anticorrosive layer without microparticles and/or nanoparticles in the layer make-up, even when the same substances are used for the anticorrosive layer.
Owing to the special anticorrosive layer, according to a development of the invention a customary steel material, which is to be understood in the present context also to mean high-grade steel material, can be used for the basic body of the casting component. This makes it possible to produce the component in a simple way, as compared with the use of ceramic materials. Moreover, already existing components having such a basic body made from steel material can easily be provided at a later stage with the anticorrosive layer. At the same time, the mechanical properties of steel which are known to be good are preserved for the casting component.
In a development of the invention, the microparticles and/or nanoparticles possess an average particle size of between 50 nm and 50 μm. In particular, average particle sizes of between 100 nm and 30 μm and especially of between 150 nm and 30 μm prove to be highly advantageous for the anticorrosive layer designed for resistance with respect to hot reactive metal melts.
In a development of the invention, the anticorrosive layer contains at least microparticles and/or nanoparticles composed of TiB2. Anticorrosive layers which are built up on the basis of these TiB2 particles and may optionally contain in addition microparticles and/or nanoparticles of one or more other substances exhibit very high corrosion resistance with respect to corrosion caused by hot Al melts.
In an advantageous development, the anticorrosive layer is a sol/gel layer, that is to say a layer applied by means of a sol/gel process, the microparticles and/or nanoparticles functioning as a filler with which the sol is loaded in the sol/gel process. Such anticorrosive layers can be applied highly uniformly and with homogeneous layer properties even on surface regions of the casting component where access is relatively difficult, this in turn being conducive, overall, to the corrosion resistance and long service life of the casting component.
In a further refinement, the sol/gel anticorrosive layer has a zirconium-based or silicon-based gel former. In a further refinement, the sol/gel anticorrosive layer contains an additionally administered alkali or alkaline earth metal salt and/or an additionally administered viscosity-setting polymer. This makes a supplementary contribution to achieving the desired good layer properties for the anticorrosive layer on corresponding melt contact surface regions of the casting component.
In a further refinement, the sol/gel anticorrosive layer is formed as a multiple layer from a plurality of coating plies, at least two of which are loaded with the microparticles and/or nanoparticles as a filler, and/or at least one layer ply, preferably the last layer ply, is applied without a filler, before all the gel layer plies are then subjected together to a baking process in the sol/gel process. By means of a multiple-ply make-up of this type, the properties of the anticorrosive layer with regard to corrosion resistance to hot metal melts can be further optimized. Thus, for example, a filler-free outer layer ply can function as a covering layer ply composed, for example, of silicon oxide or zirconium oxide. The microparticles and/or nanoparticles then remain embedded in the layer ply or layer plies lying underneath.
In a development of the invention, the casting component is intended for a device for casting an aluminum melt. By virtue of said outstanding corrosion resistance with respect to hot aluminum melts, the casting component according to the invention is eminently suitable for this intended use.
In a development of the invention, the casting component is intended for a metal diecasting machine. In particular, it may be a casting fitting, a casting vessel, a melt furnace constituent, a melt conveying constituent, a casting mold constituent or part of one of these constituents of the metal diecasting machine which come into contact with the melt. Owing to its specific anticorrosive layer, the casting component possesses eminent suitability and a comparatively long service life even for these intended uses.
By means of the method according to the invention, an anticorrosive layer is applied to a substrate by means of a sol/gel process, using microparticles and/or nanoparticles with an average particle size of between 100 nm and 50 μm as a filler. In particular, the substrate may be a casting component according to the invention, to the melt contact surface region of which the anticorrosive layer is applied. Furthermore, however, the substrate may also be any component, the surface of which has to be protected against a corrosive attack of a reactive metal melt.
In a development of the method, a plurality of gel layer plies having microparticles and/or nanoparticles of identical or different substances are formed, before the layer plies are subjected together to a curing and vitrifying baking step.
In a development of the method, a plurality of gel layer plies are formed, a filler-free sol material being used at least for a last layer ply. After a joint vitrifying baking step, the latter forms a filler-free covering layer ply, while the microparticles and/or nanoparticles remain embedded in the inner layer ply or inner layer plies.
In a development of the method, a vitrifying baking process is carried out for one or more gel layer plies at a temperature of between about 500° C. and about 650° C. It is clear that a sol/gel anticorrosion layer formed in this way, when microparticles and/or nanoparticles of suitable substances are used, has very high corrosion resistance with respect to the chemically reactive influence of hot metal melts.
Advantageous embodiments of the invention are illustrated in the drawings and are described below.